Also beware of dim traces. Short pulses in long time intervals will get too faint to be usable. John Ferrell 6241 Phillippi Rd Julian NC 27283 Phone: (336)685-9606 Dixie Competition Products NSRCA 479 AMA 4190 W8CCW "My Competition is Not My Enemy" ----- Original Message ----- From: "Roman Black" To: Sent: Wednesday, February 06, 2002 3:36 PM Subject: Re: [EE]:Oscilloscope > > >BTW, are there any "buyer beware" questions I should ask and signs I > > >should look out for while buying a used analog scope? Are there > > >certain parts that always break? How important is calibration for > > >non-critical measurements? > > Calibration is normally good on more "modern" > cros, generally anything 20MHz dual trace or 50MHz > dual trace will have ok calibration, even the cheap > asian brands. I've owned a few. > > As they age the electro caps can get ESR faults, > these change performance over time and heat. Most > typically the symptoms are that the timebase or > vertical amp will change over time, so a 10v dc > input may start ok reading 10v than read 10.5v > when the cro is hot. (or freq change) This only > takes 10 mins to test. Also check with a hard > to trigger signal and adjust the triggering so > it JUST triggers, then wait for it to get hot and > see if the triggering circuit goes iffy. > A good signal for this is a composite video from > an AV plug on a VCR etc. > > The MOST COMMON fault is "scratchy" pots, like > an audio pot they "crackle" when moved and will > cause movement or jumping of the trace. Watch the > trace while you wiggle and slowly turn the pots. > Sometimes that can be fixed by spraying with > pot cleaner, but likely they will never be perfect > again. > > Also look for any burnt-in lines across the screen > showing the cro has seen long hours of use. > :o) > -Roman > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads